Method for integrated circuit fabrication using pitch multiplication

ABSTRACT

Different sized features in the array and in the periphery of an integrated circuit are patterned on a substrate in a single step. In particular, a mixed pattern, combining two separately formed patterns, is formed on a single mask layer and then transferred to the underlying substrate. The first of the separately formed patterns is formed by pitch multiplication and the second of the separately formed patterns is formed by conventional photolithography. The first of the separately formed patterns includes lines that are below the resolution of the photolithographic process used to form the second of the separately formed patterns. These lines are made by forming a pattern on photoresist and then etching that pattern into an amorphous carbon layer. Sidewall pacers having widths less than the widths of the un-etched parts of the amorphous carbon are formed on the sidewalls of the amorphous carbon. The amorphous carbon is then removed, leaving behind the sidewall spacers as a mask pattern. Thus, the spacers form a mask having feature sizes less than the resolution of the photolithography process used to form the pattern on the photoresist. A protective material is deposited around the spacers. The spacers are further protected using a hard mask and then photoresist is formed and patterned over the hard mask. The photoresist pattern is transferred through the hard mask to the protective material. The pattern made out by the spacers and the temporary material is then transferred to an underlying amorphous carbon hard mask layer. The pattern, having features of difference sizes, is then transferred to the underlying substrate.

REFERENCE TO RELATED APPLICATIONS

This application is related to the following: U.S. patent applicationSer. No. 10/931,772 to Abatchev et al., filed Aug. 31, 2004, entitledCritical Dimension Control; U.S. patent application Ser. No. 10/932,993to Abatchev et al., filed Sep. 1, 2004, entitled Mask MaterialConversion; U.S. patent application Ser. No. 10/931,771 to Tran et al.,filed Aug. 31, 2004, entitled Methods for Increasing Photo-AlignmentMargins; and U.S. patent application Ser. 10/934,317 to Sandhu et al.,filed Sep. 2, 2004, entitled Methods to Align Mask Patterns.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to integrated circuit fabrication and,more particularly, to masking techniques.

2. Description of the Related Art

As a consequence of many factors, including demand for increasedportability, computing power, memory capacity and energy efficiency inmodern electronics, integrated circuits are continuously being reducedin size. To facilitate this size reduction, the sizes of the constituentfeatures, such as electrical devices and interconnect line widths, thatform the integrated circuits are also constantly being decreased.

The trend of decreasing feature size is evident, for example, in memorycircuits or devices such as dynamic random access memories (DRAMs),static random access memories (SRAMs), ferroelectric (FE) memories, etc.To take one example, DRAM typically comprises millions of identicalcircuit elements, known as memory cells. In its most general form, amemory cell typically consists of two electrical devices: a storagecapacitor and an access field effect transistor. Each memory cell is anaddressable location that can store one bit (binary digit) of data. Abit can be written to a cell through the transistor and read by sensingcharge on the storage electrode from the reference electrode side. Bydecreasing the sizes of constituent electrical devices and theconducting lines that access then, the sizes of the memory devicesincorporating these features can be decreased. Additionally, storagecapacities can be increased by fitting more memory cells into the memorydevices.

The continual reduction in feature sizes places ever greater demands ontechniques used to form the features. For example, photolithography iscommonly used to pattern features, such as conductive lines, on asubstrate. The concept of pitch can be used to describe the size ofthese features. Pitch is defined as the distance between an identicalpoint in two neighboring features. These features are typically definedby spacings between adjacent features, which are typically filled by amaterial, such as an insulator. As a result, pitch can be viewed as thesum of the width of a feature and of the width of the space separatingthat feature from a neighboring feature. Due to factors such as opticsand light or radiation wavelength, however, photolithography techniqueseach have a minimum pitch below which a particular photolithographictechnique cannot reliably form features. Thus, the minimum pitch of aphotolithographic technique can limit feature size reduction.

Pitch doubling is one method proposed for extending the capabilities ofphotolithographic techniques beyond their minimum pitch. Such a methodis illustrated in FIGS. 1A–1F and described in U.S. Pat. No. 5,328,810,issued to Lowrey et al., the entire disclosure of which is incorporatedherein by reference. With reference to FIG. 1A, photolithography isfirst used to form a pattern of lines 10 in a photoresist layeroverlying a layer 20 of an expendable material and a substrate 30. Asshown in FIG. 1B, the pattern is then transferred by an etch step(preferably anisotropic) to the layer 20, forming placeholders, ormandrels, 40. The photoresist lines 10 can be stripped and the mandrels40 can be isotropically etched to increase the distance betweenneighboring mandrels 40, as shown in FIG. 1C. A layer 50 of material issubsequently deposited over the mandrels 40, as shown in FIG. 1D.Spacers 60, i.e., material extending or originally formed extending fromsidewalls of another material, are then formed on the sides of themandrels 40 by preferentially etching the spacer material from thehorizontal surfaces 70 and 80 in a directional spacer etch, as shown inFIG. 1E. The remaining mandrels 40 are then removed, leaving behind onlythe spacers 60, which together act as a mask for patterning, as shown inFIG. 1F. Thus, where a given pitch formerly included a pattern definingone feature and one space, the same width now includes two features andtwo spaces defined by the spacers 60. As a result, the smallest featuresize possible with a photolithographic technique is effectivelydecreased.

It will be appreciated that while the pitch is actually halved in theexample above, this reduction in pitch is conventionally referred to aspitch “doubling,” or, more generally, pitch “multiplication.” That is,conventionally “multiplication” of pitch by a certain factor actuallyinvolves reducing the pitch by that factor. The conventional terminologyis retained herein.

Because the layer 50 of spacer material typically has a single thickness90 (see FIGS. 1D and 1E) and because the sizes of the features formed bythe spacers 60 usually corresponds to that thickness 90, pitch doublingtypically produces features of only one width. Circuits, however, oftenemploy features of different sizes. For example, random access memorycircuits typically contain arrays of memory cells and logic circuits inthe so-called “periphery.” In the arrays, the memory cells are typicallyconnected by conductive lines and, in the periphery, the conductivelines typically contact landing pads for connecting arrays to logic.Peripheral features such as landing pads, however, can be larger thanthe conductive lines. In addition, periphery electrical devices such astransistors can be larger than electrical devices in the array.Moreover, even if peripheral features can be formed with the same pitchas the array, the flexibility required to define circuits will typicallynot be possible using a single mask, particularly if the patterns arelimited to those that can be formed along the sidewalls of patternedphotoresist.

Some proposed methods for forming patterns at the periphery and at thearray involve etching a pattern into the array region of a substrate andinto periphery of the substrate separately. Thus, a pattern in the arrayis first formed and transferred to the substrate using one mask and thenanother pattern in the periphery is formed and separately transferred tothe substrate using another mask. Because such methods form patternsusing different masks at different locations on a substrate, they arelimited in their ability to form features that require overlappingpatterns, such as when a landing pad overlaps an interconnect line, andyet a third mask may be necessitated to “stitch” two separate patternswith interconnects. Additionally, such a third mask would face evengreater challenges with respect to mask alignment due to the finefeatures defined by the pitch multiplication technique.

Accordingly, there is a need for methods of forming features ofdifferent sizes, especially where the features require differentoverlapping patterns and especially in conjunction with pitchmultiplication.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method is provided forsemiconductor processing. The method comprises providing a substratehaving a primary mask layer overlying the substrate, a temporary layeroverlying the primary mask layer and a first photoresist layer overlyingthe temporary layer. A photoresist pattern is formed in the firstphotoresist layer. A first pattern, having features derived fromfeatures of the photoresist pattern, is formed in the temporary layer. Asecond photoresist layer is subsequently formed above the level of thefirst pattern and an other photoresist pattern is formed in the secondphotoresist layer. The other photoresist pattern and the first patternare transferred to the primary mask layer to form a mixed pattern in theprimary mask layer. The substrate is processed through the mixed patternin the primary mask layer. It will be appreciated that the substrate cancomprise any material or materials to be processed through the primarymasking layer.

According to another aspect of the invention, a method is provided forforming an integrated circuit. The method comprises providing asubstrate and forming an amorphous carbon layer over the substrate. Afirst hard mask layer is formed over the first amorphous carbon layer. Atemporary layer is formed over the first hard mask layer and a secondhard mask layer is formed over the temporary layer.

According to another aspect of the invention, a method is provided forsemiconductor fabrication. The method comprises forming a first patternby pitch multiplication and separately forming a second pattern byphotolithography without pitch multiplication. The first and secondpatterns are transferred to a mask layer and a substrate is etchedthrough the mask layer.

According to yet another aspect of the invention, a method is providedfor forming an integrated circuit. The method comprises forming a maskpattern in which a first part of the mask pattern has a first pitch anda second part of the mask pattern has a second pitch. The first pitch isbelow a minimum pitch of a photolithographic technique for defining thesecond pattern. The method also comprises etching a substrate throughthe mask pattern.

According to another aspect of the invention, a method is provided forforming a memory device. The method comprises forming a pattern oftemporary placeholders in a layer over a first carbon layer. A layer ofmask material is deposited over surfaces of the temporary placeholdersand is then selectively removed from horizontal surfaces of the memorydevice. The temporary placeholders are selectively removed relative tothe mask material to form a pattern of mask material corresponding tofeatures in an array region of the memory device.

According to yet another aspect of the invention, a method is providedfor for manufacturing an integrated circuit. The method comprisesforming a plurality of mandrel strips. A spacer is formed on sidewallsof each mandrel strip. The mandrel strips are removed to form a patternof spaced apart spacers. A mask layer is formed in a plane above thespacers and a pattern is formed in the mask layer. The pattern istransferred to the same horizontal plane as the spacers.

According to another aspect of the invention, a method is provided formanufacturing an integrated circuit. The method comprises providing aplurality of spaced-apart lines of a mask material above a substrate,where the mask material is different from photoresist. A plurality offeatures is defined in a photodefinable material above the substrate bya photolithographic technique. The spaced-apart lines and the pluralityof features are replicated in an amorphous carbon layer below thespaced-apart lines.

According to another aspect of the invention, a method is provided forforming a mask pattern to fabricate an integrated circuit. The methodcomprises providing a plurality of lines of a first mask material. Thelines are separated by a first temporary material. The first temporarymaterial is selectively etched. Spaces between the lines are filled witha second temporary material. The second temporary material isselectively etched to open the spaces. A pattern is then formed in alayer of another mask material below the plurality of lines byselectively etching through the spaces.

According to another aspect of the invention, a process is provided forfabricating an integrated circuit. The process comprises providing amasking layer extending over a first and a second region of a partiallyfabricated integrated circuit. A pattern is formed in the masking layer.A minimum feature size of a portion of the pattern corresponding to thefirst region is equal to or less than about half a minimum feature sizeof an other portion of the pattern corresponding to the second region.

According to another aspect of the invention, a partially formedintegrated circuit is provided. The partially formed integrated circuitcomprises a carbon layer and a plurality of pitch-multiplied spacers ona level overlying the carbon layer. The spacers have a pitch of about100 nm or less.

According to yet another aspect of the invention, a partially formedintegrated circuit is provided. The partially formed integrated circuitcomprises a substrate and a primary mask layer overlying the substrate.The primary mask layer formed of a material different from photoresist.A mask material defining a first pattern is disposed in a first planeoverlying the primary mask layer. A photodefinable material defining asecond pattern is disposed in a second plane overlying the maskmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIGS. 1A–1F are schematic, cross-sectional side views of partiallyformed conductive lines, formed in accordance with a prior art pitchdoubling method;

FIGS. 2A–2B are a schematic, cross-sectional top and side views of apartially formed memory device, in accordance with preferred embodimentsof the invention;

FIG. 3 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 2 after forming lines in a selectively definablelayer in the array of the memory device, in accordance with preferredembodiments of the invention;

FIG. 4 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 3 after widening spaces between photoresist lines,in accordance with preferred embodiments of the invention;

FIG. 5 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 4 after etching through a hard mask layer, inaccordance with preferred embodiments of the invention;

FIG. 6 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 5 after transferring a pattern from thephotoresist layer to a temporary layer, in accordance with preferredembodiments of the invention;

FIG. 7 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 6 after depositing a layer of a spacer material,in accordance with preferred embodiments of the invention;

FIG. 8 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 7 after a spacer etch, in accordance withpreferred embodiments of the invention;

FIG. 9 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 8 after removing a remaining portion of thetemporary layer to leave a pattern of spacers in the array of the memorydevice, in accordance with preferred embodiments of the invention;

FIG. 10 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 9 after surrounding the spacers with aremovable material and forming a hard mask layer and a selectivelydefinable layer over the spacers, in accordance with preferredembodiments of the invention;

FIG. 11 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 10 after forming a pattern in theselectively definable layer in the periphery of the memory device, inaccordance with preferred embodiments of the invention;

FIG. 12 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 11 after etching through the top hard masklayer, in accordance with preferred embodiments of the invention;

FIG. 13 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 12 after transferring the pattern from theselectively definable layer to the same level as the spacers, inaccordance with preferred embodiments of the invention;

FIG. 14 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 13 after etching the pattern in theperiphery and the spacer pattern in the array into an underlying hardmask layer, in accordance with preferred embodiments of the invention;

FIG. 15 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 14 after transferring the pattern in theperiphery and the spacer pattern in the array together to a primary masklayer, in accordance with preferred embodiments of the invention;

FIG. 16 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 15 after transferring the periphery patternand the spacer pattern to the underlying substrate, in accordance withpreferred embodiments of the invention; and

FIGS. 17A and 17B are micrographs, as viewed through a scanning electronmicroscope, of a pattern etched into the array and the periphery,respectively, of a partially formed memory device, formed in accordancewith preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In addition to problems with forming different size features, it hasbeen found that pitch doubling techniques can have difficultytransferring spacer patterns to a substrate. In particular, in commonmethods of transferring patterns, both the spacers and the underlyingsubstrate are exposed to an etchant, which preferentially etches awaythe substrate material. It will be appreciated, however, that theetchants also wear away the spacers, albeit at a slower rate. Thus, overthe course of transferring a pattern, the spacers can be worn away bythe etchant before the pattern transfer is complete. These difficultiesare exacerbated by the trend towards decreasing feature size, which, forexample, increasingly leads to higher aspect ratios as the widths ofthese trenches decrease. In conjunction with difficulties of producingstructures of different feature sizes, these pattern transferlimitations make even more difficult the application of pitch-doublingprinciples to integrated circuit manufacture.

In view of these difficulties, preferred embodiments of the inventionallow for improved pattern transfer and for the formation of differentsize features in conjunction with pitch doubling. In a first phase ofthe method, photolithography and pitch doubling are preferably used toform a spacer pattern. This typically forms features of one size in oneregion of the chip, e.g., the array of a memory chip. In a second phase,photolithography is again performed to form a second pattern in anotherregion of the chip, e.g., the periphery of the memory chip, in a layeroverlying the spacer pattern. Both the spacer pattern and the secondpattern are then transferred to an underlying primary masking layer,which preferably can be preferentially etched relative to an underlyingsubstrate. The spacer and second patterns are then transferred from theprimary masking layer to the underlying substrate in a single step.Thus, patterns for forming different size features, some of which arebelow the minimum pitch of the photolithographic technique used forpatterning, can be formed and these patterns can be successfullytransferred to the underlying substrate.

Moreover, because the second pattern is initially formed on a layeroverlying the spacer pattern, the second pattern can overlap the spacerpattern. As a result, overlapping features of different sizes, such asconducting lines and landing pads or periphery transistors, canadvantageously be formed.

Preferably, the primary masking layer is the masking layer that directlyoverlies and, due to etch selectivity, is primarily used to perform aprocess (e.g., etch) on the substrate through the primary masking layer.In particular, the primary masking layer is preferably formed of amaterial that allows good etch selectivity relative to both the spacermaterial and the substrate material, so that spacer pattern caneffectively be transferred to it; so that the primary masking layer canbe selectively removed after processing without harming the substrate;and, when the mask is used for etching the substrate, so that thepattern in it can effectively be transferred to the substrate. Due toits excellent etch selectivity relative to a variety of materials,including oxides, nitrides and silicon, the primary masking layer ispreferably formed of carbon and, more preferably, amorphous carbon.

It will be appreciated that a substrate can comprise any material ormaterials that are to be processed through the primary masking layer.Thus, a substrate can include a layer of a single material, a pluralityof layers of different materials, a layer or layers having regions ofdifferent materials or structures in them, etc. These materials caninclude semiconductors, insulators, conductors, or combinations thereof.Typically, the substrate comprises structures or layers ultimately formpart of the integrated circuit being fabricated.

It will also be appreciated that transferring a pattern from a firstlevel to a second level involves forming features in the second levelthat generally correspond to features on the first level. For example,the path of lines in the second level will generally follow the path oflines on the first level and the location of other features on thesecond level will correspond to the location of similar features on thefirst level. The precise shapes and sizes of features can vary from thefirst level to the second level, however. For example, depending uponetch chemistries and conditions, the sizes of and relative spacingsbetween the features forming the transferred pattern can be enlarged ordiminished relative to the pattern on the first level, while stillresembling the same initial “pattern.”

Reference will now be made to the Figures, wherein like numerals referto like parts throughout. It will be appreciated that FIGS. 2–16 are notnecessarily drawn to scale.

While the preferred embodiments will find application in any context inwhich features of different sizes are formed on a substrate, inparticularly advantageous embodiments, part of the pattern to betransferred to a substrate is formed by pitch multiplication and thathas a pitch below the minimum pitch of the photolithographic techniqueused for processing the substrate. In addition, while the preferredembodiments can be used to form any integrated circuit, they areparticularly advantageously applied to form devices having arrays ofelectrical devices, including logic or gate arrays and volatile andnon-volatile memory devices such as DRAM, ROM or flash memory. In suchdevices, pitch multiplication can be used to form, e.g., transistor gateelectrodes and conductive lines in the array region of the chips, whileconventional photolithography can be used to form larger features, suchas contacts, at the peripheries of the chips. Exemplary masking steps inthe course of fabricating a memory chip are illustrated in the Figures.

FIG. 2A shows a top view of a partially fabricated integrated circuit,or memory chip, 100. A central region 102, the “array,” is surrounded bya peripheral region 104, the “periphery.” It will be appreciated that,after fabrication of the integrated circuit 100 is complete, the array102 will typically be densely populated with conducting lines andelectrical devices such as transistors and capacitors. Desirably, pitchmultiplication can be used to form features in the array 102, asdiscussed below. On the other hand, the periphery 104 can have featureslarger than those in the array 102. Conventional photolithography,rather than pitch multiplication, is typically used to pattern thesefeatures, because the geometric complexity of logic circuits located inthe periphery 104 makes using pitch multiplication difficult. Inaddition, some devices in the periphery require larger geometries due toelectrical constraints, thereby making pitch multiplication lessadvantageous than conventional photolithography for such devices.

With reference to FIG. 2B, a partially formed integrated circuit 100 isprovided. A substrate 110 is provided below various layers 120–160. Thesubstrate 110 will be patterned to form various features and the layers120–160 will be etched to form a mask for the pattern, as discussedbelow. The materials for the layers overlying the substrate 110 arepreferably chosen based upon consideration of the chemistry and processcondition requirements for the various pattern forming and patterntransferring steps discussed herein. Because the layers between atopmost selectively definable layer 120, which preferably is definableby a lithographic process, and the substrate 110 function to transfer apattern derived from the selectively definable layer 120 to thesubstrate 110, the layers between the selectively definable layer 120and the substrate 110 are preferably chosen so that they can beselectively etched relative to other exposed materials during theiretch. It will be appreciated that a material is considered selectively,or preferentially, etched when the etch rate for that material is atleast about 5 times greater, preferably about 10 times greater, morepreferably about 20 times greater and, most preferably, at least about40 times greater than that for surrounding materials.

In the illustrated embodiment, the selectively definable layer 120overlies a first hard mask, or etch stop, layer 130, which overlies atemporary layer 140, which overlies a second hard mask, or etch stop,layer 150, which overlies a primary mask layer 160, which overlies thesubstrate 110 to be processed (e.g., etched) through a mask. Thethicknesses of the layers are preferably chosen depending uponcompatibility with the etch chemistries and process conditions describedherein. For example, when transferring a pattern from an overlying layerto an underlying layer by selectively etching the underlying layer,materials from both layers are removed to some degree. Thus, the upperlayer is preferably thick enough so that it is not worn away over thecourse of the etch.

In the illustrated embodiment, the first hard mask layer 130 ispreferably between about 10–50 nm thick and, more preferably, betweenabout 10–30 nm thick. The temporary layer 140 is preferably betweenabout 100–300 nm thick and, more preferably, between about 100–200 nmthick. The second hard mask layer 150 is preferably between about 10–50nm thick and, more preferably, about 20–40 nm thick and the primary masklayer 160 is preferably between about 100–1000 nm thick and, morepreferably, about 100–500 nm thick.

With reference to FIG. 2, the selectively definable layer 120 ispreferably formed of a photoresist, including any photoresist known inthe art. For example, the photoresist can be any photoresist compatiblewith 13.7 nm, 157 nm, 193 nm, 248 nm or 365 nm wavelength systems, 193nm wavelength immersion systems or electron beam lithographic systems.Examples of preferred photoresist materials include argon fluoride (ArF)sensitive photoresist, i.e., photoresist suitable for use with an ArFlight source, and krypton fluoride (KrF) sensitive photoresist, i.e.,photoresist suitable for use with a KrF light source. ArF photoresistsare preferably used with photolithography systems utilizing relativelyshort wavelength light, e.g., 193 nm. KrF photoresists are preferablyused with longer wavelength photolithography systems, such as 248 nmsystems. In other embodiments, the layer 120 and any subsequent resistlayers can be formed of a resist that can be patterned by nano-imprintlithography, e.g., by using a mold or mechanical force to pattern theresist.

The material for the first hard mask layer 130 preferably comprises asilicon oxide (SiO₂), silicon or a dielectric anti-reflective coating(DARC), such as a silicon-rich silicon oxynitride. DARCs can beparticularly advantageous for forming patterns having pitches near theresolution limits of a photolithographic technique because they canenhance resolution by minimizing light reflections. It will beappreciated that light reflections can decrease the precision with whichphotolithography can define the edges of a pattern. Optionally, a bottomanti-reflective coating (BARC) (not shown) can similarly be used inaddition to the first hard mask layer 130 to control light reflections.

The temporary layer 140 is preferably formed of amorphous carbon, whichoffers very high etch selectivity relative to the preferred hard maskmaterials. More preferably, the amorphous carbon is a form oftransparent carbon that is highly transparent to light and which offersfurther improvements for photo alignment by being transparent towavelengths of light used for such alignment. Deposition techniques forforming a highly transparent carbon can be found in A. Helmbold, D.Meissner, Thin Solid Films, 283 (1996) 196–203, the entire disclosure ofwhich is incorporated herein by reference.

As with the first hard mask layer 130, the second hard mask layer 150preferably comprises a dielectric anti-reflective coating (DARC) (e.g.,a silicon oxynitride), a silicon oxide (SiO₂) or silicon. In addition, abottom anti-reflective coating (BARC) (not shown) can also optionally beused to control light reflections. While the first and the second hardmask layers 130 and 150 can be formed of different materials, theselayers are preferably formed of the same material for ease of processingand to minimize the number of different etch chemistries utilized, asdescribed below. Like the temporary layer 140, the primary mask layer160 is preferably formed of amorphous carbon and, more preferably,transparent carbon.

It will be appreciated that the various layers discussed herein can beformed by various methods known to those of skill in the art. Forexample, various vapor deposition processes, such as chemical vapordeposition can be used to form the hard mask layers. Preferably, a lowtemperature chemical vapor deposition process is used to deposit thehard mask layers or any other materials, e.g., spacer material (FIG. 7),over the mask layer 160, where the mask layer 160 is formed of amorphoussilicon. Such low temperature deposition processes advantageouslyprevent chemical or physical disruption of the amorphous carbon layer.

Spin-on-coating processes can be used to form the photodefinable layers.In addition, amorphous carbon layers can be formed by chemical vapordeposition using a hydrocarbon compound, or mixtures of such compounds,as carbon precursors. Exemplary precursors include propylene, propyne,propane, butane, butylene, butadiene and acetelyne. A suitable methodfor forming amorphous carbon layers is described in U.S. Pat. No.6,573,030 B1, issued to Fairbaim et al. on Jun. 3, 2003, the entiredisclosure of which is incorporated herein by reference.

In a first phase of the method in accordance with the preferredembodiments and with reference to FIGS. 3–9, pitch multiplication in thearray of the partially formed integrated circuit 100 is performed. Apattern is formed on the photodefinable layer 120, as shown in FIG. 3.The photodefinable layer 120 can be patterned by, e.g.,photolithography, in which the layer 120 is exposed to radiation througha reticle and then developed. After being developed, the remainingphotodefinable material, photoresist in this case, comprises lines 122,which define spaces 124.

As shown in FIG. 4, the widths of the spaces 122 and the photoresistlines 122 can be altered to a desired dimension. For example, the spaces122 can be widened by etching the photoresist lines 124. The photoresistlines 124 are preferably etched using an isotropic etch, such as asulfur oxide plasma, e.g., a plasma comprising SO₂, O₂, N₂ and Ar. Theextent of the etch is preferably selected so that a resulting line 124 ahas a width corresponding to the desired spacing of the spacers to beformed, as will be appreciated from the discussion below with respect toFIGS. 8–16. Advantageously, in addition to allowing the formation oflines 124 a that are narrower than features defined by thephotolithographic technique used to pattern the photodefinable layer120, this etch can smooth the edges of the lines 124 thereby improvingthe uniformity of the lines 124. The resulting photoresist lines 124 and124 a thus constitute the placeholders or mandrels upon which a patternof spacers 175 (FIG. 9) will be formed. In other embodiments, the spacesbetween the spaces 122 can be narrowed by expanding the lines 124 to adesired size. For example, additional material can be deposited over thelines 124 or the lines 124 can be chemically reacted to form a materialhaving a larger volume to increase their size.

The pattern of the (modified) photodefinable layer 120 is preferablytransferred to a layer 140 of material that can withstand with theprocess conditions for spacer material deposition, discussed below. Inaddition to having higher heat resistance than photoresist, the materialforming the temporary layer 140 is preferably selected such that it canbe selectively removed relative to the spacer material and theunderlying layer. As noted above, the layer 140 is preferably formed ofamorphous carbon. Because the preferred chemistries for etchingphotoresist also typically etch significant amounts of amorphous carbonand because chemistries are available for etching amorphous carbon withexcellent selectivity relative to a variety of materials, a hard masklayer 130 selected from such materials preferably separates the layers120 and 140. Suitable materials for the hard mask layer 130 include, forexample, DARCs, silicon oxides or nitrides, and silicon.

The pattern in the photodefinable layer 120 is preferably transferred tothe hard mask layer 130, as shown in FIG. 5. This transfer is preferablyaccomplished using an anisotropic etch, such as an etch using afluorocarbon plasma, although a wet (isotropic) etch may also besuitable if the hard mask layer 130 is thin. Preferred fluorocarbonplasma etch chemistries can include CF₄, CFH₃, CF₂H₂, CF₃H, etc.

The pattern is then transferred to the temporary layer 140, as shown inFIG. 6, preferably using a SO₂-containing plasma, e.g., a plasmacontaining SO₂, O₂ and Ar. Advantageously, the SO₂-containing plasma canetch carbon of the preferred temporary layer 140 at a rate greater than20 times and, more preferably, greater than 40 times the rate that thehard mask layer 130 is etched. A suitable SO₂-contaiing plasma isdescribed in U.S. patent application Ser. No. 10/931,772 to Abatchev etal., filed Aug. 31, 2004, entitled Critical Dimension Control, theentire disclosure of which is incorporate herein by reference. It willbe appreciated that the SO₂-containing plasma simultaneously etches thetemporary layer 140 and removes the photodefinable layer 120.

As shown in FIG. 7, a layer 170 of spacer material is preferably nextdeposited over the hard mask layer 130 and the temporary layer 140. Thespacer material is preferably deposited by chemical vapor deposition oratomic layer deposition. The spacer material can be any material capableof use as a mask to transfer a pattern to the underlying primary masklayer 160. The spacer material preferably: 1) can be deposited with goodstep coverage, 2) can be deposited at a low temperature compatible withthe temporary layer 140 and 3) can be selectively etched relative to thetemporary layer 140 and any layer underlying the temporary layer 140.Preferred materials include silicon nitrides and silicon oxides.

As shown in FIG. 8, the spacer layer 170 is then subjected to ananisotropic etch to remove spacer material from horizontal surfaces 180of the partially formed integrated circuit 100. Such an etch, also knownas a spacer etch, can be performed using a fluorocarbon plasma, whichcan also advantageously etch the hard mask layer 130. Next, theamorphous carbon layer 140 can be selectively removed, using, e.g., aSO₂-containing plasma. FIG. 9 shows a pattern of spacers 175 left afterthe amorphous carbon etch. Thus, pitch multiplication in the array ofthe partially formed integrated circuit 100 has been accomplished and,in the illustrated embodiment, the pitch of the spacers is half that ofthe photoresist lines 124 (FIG. 3) originally formed byphotolithography. It will be appreciated that the spacers 175 generallyfollow the outline of the pattern or lines 124 originally formed in thephotodefinable layer 120.

Next, in a second phase of a method according to the preferredembodiments, a second pattern is formed at the periphery 104. To formthis second pattern, the spacers 175 are protected and anotherphotodefinable layer 220 is formed, as shown in FIG. 10, to allow forpatterning of the second pattern at the periphery 104. The spacers 175are protected by forming a protective layer 200 over the spacers 175.The protective layer 200 is preferably at least as tall as the spacers175 and preferably about 100–500 nm thick and, more preferably, about100–300 nm thick. A hard mask layer 210 is next preferably formed overthe protective layer 200 to aid in transferring a pattern from thephotodefinable layer 220 to the protective layer 200. Preferably, thehard mask layer 210 is about 40–80 nm thick and, more preferably, about50–60 nm thick.

The protective layer 200 is preferably formed of a material that isreadily removed selectively relative to the spacers 175. For example,the protective layer 200 can be formed of a photoresist, and may be thesame or a different photoresist from that used to form thephotodefinable layer 120 (FIGS. 2–5), which can be the same or adifferent material from than used to form the photodefinable layer 220(FIG. 10). More preferably, the protective layer 200 is formed ofamorphous carbon, which can be etched with excellent selectivityrelative to the spacers 175.

In other embodiments where the protective layer 200 is formed of amaterial that can be selectively etched relative to both the spacers 175and the photodefinable layer 220, the hard mask layer 210 can beomitted. For example, the protective layer 200 can be formed of a bottomanti-reflective coating (BARC) and a photoresist can be formed directlyabove the BARC. The spacers 175 can be formed of a material which allowsgood etch selectivity to the BARC, including silicon nitrides or oxides.

While it can be patterned using any photolithographic technique, thephotodefinable layer 220 is preferably patterned using the samephotolithographic technique used to pattern the photodefinable layer120. Thus, with reference to FIG. 11, a pattern 230 is formed in thephotodefinable layer 220. While the pattern 177 preferably has a pitchor resolution smaller than the minimum pitch or resolution of thephotolithographic technique, the pattern 230 preferably has a pitch orresolution equal to or greater than the minimum pitch or resolution ofthe photolithographic technique. It will be appreciated that the pattern230 at the periphery 104 can be used to form landing pads, transistors,local interconnects etc. It will also be appreciated that, whileillustrated laterally separated from the pattern 177, the pattern 230can also overlap the pattern 177. Thus, the use of different referencenumerals (177 and 230) for these patterns indicates that they wereoriginally formed in different steps.

The pattern 230 is then transferred to the same level as the pattern 177of spacers 175. As shown in FIG. 12, the hard mask layer 210 isselectively etched relative to the photodefinable layer 220, preferablyusing an anisotropic etch such as a fluorocarbon plasma etch.Alternatively, a wet (isotropic) etch may also be suitable for the hardmask layer 210 is appropriately thin. The pattern 230 is thentransferred to the protective layer 200 by another anisotropic etch,such as an etch with a SO₂-containing plasma, as shown in FIG. 13.Because the hard mask layer 210 overlying the spacers 175 has previouslybeen removed, this etch also removes the protective layer 200 around thespacers 175, thereby leaving those spacers 175 exposed.

With reference to FIGS. 14 and 15, the patterns 177 and 230 are thentransferred down to the primary mask layer 160, which preferablycomprises a material having good etch selectivity to the substrate 110,and vice versa, to allow the patterns 177 and 230 to be simultaneouslytransferred to the substrate 110. Thus, the patterns 177 and 230 form amixed pattern in the primary mask layer 160.

To transfer to the patterns 177 and 230, the hard mask layer 150overlying the primary mask layer 160 is first etched (FIG. 14). The hardmask layer 150 is preferably anisotropically etched, preferably using afluorocarbon plasma. Alternatively, an isotropic etch may be used if thehard mask layer 150 is relatively thin.

The primary mask layer 160 is then anisotropically etched, preferablyusing a SO₂-containing plasma, which can simultaneously remove thephotodefinable layer 200 (FIG. 15). As noted above, the SO₂-containingplasma has excellent selectivity for the amorphous carbon of the primarymask layer 160 relative to the hard mask layer 150. Thus, a thick enoughmask can be formed in the primary mask layer 160 to later effectivelytransfer the mask pattern to the substrate 110 using conventional etchchemistries and without wearing away the primary mask layer 160 beforethe pattern transfer is complete.

Having both been transferred to the primary mask layer 160, the patterns177 and 230 can then be transferred to the subtrate 110 using the layer160 as a mask, as illustrated in FIG. 16. Given the disparate materialstypically used for the primary mask layer 160 and the substrate 110(e.g., amorphous carbon and silicon or silicon compounds, respectively),the pattern transfer can be readily accomplished using conventionaletches appropriate for the material or materials comprising thesubstrate 110. For example, a fluorocarbon etch comprising CF₄, CHF₃and/or NF₃ containing plasma can be used to etch silicon nitride, afluorocarbon etch comprising CF₄, CHF₃, CH₂F₂ and/or C₄F₈ containingplasma can be used to etch silicon oxide and a HBr, Cl₂, NF₃, SF₆ and/orCF₄ containing plasma etch can be used to etch silicon. In addition, theskilled artisan can readily determine suitable etch chemistries forother substrate materials, such as conductors, including aluminum,transition metals, and transition metal nitrides. For example, analuminum substrate can be etched using a fluorocarbon etch.

It will be appreciated that where the substrate 110 comprises layers ofdifferent materials, a succession of different chemistries, preferablydry-etch chemistries, can be used to successively etch through thesedifferent layers. It will also be appreciated that, depending upon thechemistry or chemistries used, the spacers 175 and the hard mask layer150 may be etched. Amorphous carbon of the primary mask layer 160,however, advantageously offers excellent resistance to conventional etchchemistries, especially those used for etching silicon-containingmaterials. Thus, the primary mask layer 160 can effectively be used as amask for etching through a plurality of substrate layers, or for forminghigh aspect ratio trenches. In addition, the pitch doubled pattern 177and the pattern 230 formed by conventional lithography cansimultaneously be transferred to the substrate 110, or each individuallayer of the substrate 110, in a single etch step.

FIGS. 17A and 17B show the resultant structure. FIG. 17A shows the arrayportion of the integrated circuit 100, while FIG. 17B shows theperiphery of the integrated circuit 100 (FIGS. 2–16). As noted above,the substrate 110 can be any layer of material or materials that thepatterns 177 and 230 are etched into. The composition of the substrate110 can depend upon, e.g., the electrical device to be formed. Thus, inFIGS. 17A and 17B, the substrate 110 comprises a Si₃N₄ layer 110 a, apolysilicon layer 110 b, a SiO₂ layer 110 c and a silicon layer 110 d.Such an arrangement of layers can be advantageously used in theformation of, e.g., transistors.

Note that the etched surfaces exhibit exceptionally low edge roughness.In addition, the trenches formed in the array show excellent uniformity,even at the low 100 nm pitch pictured. Advantageously, these results areachieved while also forming well-defined and smooth lines in theperiphery, as illustrated in FIG. 17B.

It will be appreciated that the formation of patterns according to thepreferred embodiments offers numerous advantages. For example, becausemultiple patterns, with different size features, can be consolidated ona single final mask layer before being transferred to a substrate,overlapping patterns can easily be transferred to the substrate. Thus,pitch-doubled features and features formed by conventionalphotolithography can easily be formed connected to each other. Moreover,as evident in FIGS. 17A and 17B, exceptionally small features can beformed, while at the same time achieving exceptional and unexpectedlylow line edge roughness. While not limited by theory, it is believedthat such low line edge roughness is the result of the use of the layers140 and 160. Forming the spacers 175 and performing multiple anisotropicetches to transfer the patterns 177 and 230 from the level of thetemporary layer 140 to the primary mask layer 160 and then to thesubstrate 110 are believed to beneficially smooth the surfaces of thefeatures forming the patterns 177 and 230. Moreover, the preferredamorphous carbon etch chemistries disclosed herein allow the use of thinhard mask layers, such as the layers 130 and 150, relative to the depththat underlying amorphous carbon layers, such as the layers 140 and 160,are etched. This advantageously reduces demands on the identity oflayers (e.g., photoresist layers) overlying the hard mask layers andalso reduces demands on the chemistries used to etch the hard masklayers while at the same time ensuring that the primary mask layers formthick enough masks to withstand subsequent substrate etches.

It will also be appreciated that various modifications of theillustrated process flow are possible. For example, pitch multipliedpatterns typically formed closed loops, since the patterns are formed byspacers that surround a mandrel. Consequently, where the pitchmultiplied pattern is used to form conductive lines, additionalprocessing steps are preferably used to cut off the ends of these loops,so that each loop forms two individual, non-connected lines.

Also, while the composition of the various layers discussed herein ischosen based upon consideration of etch chemistries and processconditions, the various hard mask layers are preferably each formed ofthe same material, as are the primary mask layers. Advantageously, suchan arrangement reduces processing complexity.

In addition, the pitch of the pattern 177 can be more than doubled. Forexample, the pattern 177 can be further pitch multiplied by formingspacers around the spacers 175, then removing the spacers 175, thenforming spacers around the spacers that were formerly around the spacersthe 175, and so on. An exemplary method for further pitch multiplicationis discussed in U.S. Pat. No. 5,328,810 to Lowrey et al. In addition,while the preferred embodiments can advantageously be applied to formedpatterns having both pitch multiplied and conventionallyphotolithographically defined features, the patterns 177 and 230 canboth be pitch multiplied or can have different degrees of pitchmultiplication.

Moreover, more than two patterns 177 and 230 can be consolidated on theprimary mask layer 160 if desired. In such cases, additional mask layerscan be deposited between the layers 140 and 160. For example, thepatterns 177 and 230 can be transferred to an additional mask layeroverlying the hard mask layer 150 and then the sequence of stepsillustrated in FIGS. 10–16 can be performed to protect the patterns 77and 230, to form the new pattern in an overlying photodefinable layerand to transfer the patterns to the substrate 110. The additional masklayer preferably comprises a material that can be selectively etchedrelative to the hard mask layer 150 and a protective layer thatsurrounds the patterns 177 and 230 after being transferred to theadditional mask layer.

Also, while “processing” through the various mask layers preferablyinvolve etching an underlying layer, processing through the mask layerscan involve subjecting layers underlying the mask layers to anysemiconductor fabrication process. For example, processing can involveion implantation, diffusion doping, depositing, or wet etching, etc.through the mask layers and onto underlying layers. In addition, themask layers can be used as a stop or barrier for chemical mechanicalpolishing (CMP) or CMP can be performed on the mask layers to allow forboth planarizing of the mask layers and etching of the underlyinglayers,

Accordingly, it will be appreciated by those skilled in the art thatvarious other omissions, additions and modifications may be made to themethods and structures described above without departing from the scopeof the invention. All such modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

1. A method for semiconductor processing, comprising: providing asubstrate, wherein a primary mask layer overlies the substrate, whereina temporary layer overlies the primary mask layer, wherein a firstphotoresist layer overlies the temporary layer; forming a photoresistpattern in the first photoresist layer; forming a first pattern in thetemporary layer, wherein features of the first pattern are derived fromfeatures of the photoresist pattern; forming a second photoresist layerabove a level of the first pattern; forming an other photoresist patternin the second photoresist layer; transferring the other photoresistpattern and the first pattern to the primary mask layer to form a mixedpattern in the primary mask layer; and processing the substrate throughthe mixed pattern in the primary mask layer.
 2. The method of claim 1,wherein processing the substrate comprises transferring the mixedpattern to the substrate by etching the substrate.
 3. The method ofclaim 1, wherein forming a photoresist pattern and/or forming an otherphotoresist pattern comprise performing electron beam lithography. 4.The method of claim 1, wherein forming a photoresist pattern and formingan other photoresist pattern comprise performing photolithography withlight having a wavelength chosen from the group consisting of 13.7 nm,157 nm, 193 nm, 248 nm or 365 nm wavelength light.
 5. The method ofclaim 4, wherein the first and the second photoresist layer comprise thesame photoresist material.
 6. The method of claim 4, wherein forming thefirst pattern further comprises reducing a width of the photoresist,remaining after performing photolithography, to a desired width byisotropically etching the photoresist.
 7. The method of claim 6, whereinthe first pattern follows an outline of lines of photoresist remainingafter isotropically etching, wherein forming the first patterncomprises: etching the temporary layer through the photoresist layer;forming spacers on sidewalls of remains of the temporary layer afteretching the temporary layer; and preferentially removing temporary layermaterial relative to the spacers, wherein the spacers form the firstpattern.
 8. The method of claim 1, wherein the temporary layer comprisesamorphous carbon.
 9. The method of claim 8, wherein the primary masklayer comprises amorphous carbon.
 10. The method of claim 9, whereinhard mask layers directly overlie the temporary layer and the primarymask layer.
 11. The method of claim 10, wherein the hard mask layerscomprise a material selected from the group consisting of silicon,silicon dioxide or an antireflective coating material.
 12. The method ofclaim 11, wherein the antireflective coating material is a dielectricantireflective coating.
 13. The method of claim 1, wherein the temporarylayer comprises a bottom anti-flective coating.
 14. The method of claim13, wherein the second photoresist layer directly contacts and overliesthe bottom anti-flective coating.
 15. The method of claim 1, wherein thesubstrate is an insulator.
 16. The method of claim 15, whereinprocessing the substrate defines conductive lines of an array of amemory device.